Among the conventionally-known oil level detecting switches or oil level detectors are ones in which a float moves up or down, in response to variation of an oil level, while being guided by a guide rod (see, for example, Japanese Utility Model Laid-Open Publication No. SHO-62-133132 that will hereinafter be referred to as “Patent Literature 1”), and ones in which a movable contact is provided at the lower end of a float and in which, as the float descends, the movable contact contacts and electrically connects to the two fixed contacts (see, for example, Japanese Utility Model Laid-Open Publication No. HEI-5-14507 that will hereinafter be referred to as “Patent Literature 2”).
According to the disclosure of Patent Literature 1, a wave preventing case is provided in a crankcase, a bottom plate is mounted on a lower portion of the wave preventing case, a guide rod extends upwardly from the bottom plate within the wave preventing case, and a float is fitted in the guide rod in such a manner that it is movable up and down. Proximity switch for detecting a position of the float is incorporated in the guide rod. However, because the guide rod is located centrally in the oil level detector as viewed in plan and extends through the float, the oil level detector would have to be increased in overall size as the outer diameter of the guide rod is increased. Further, because the guide rod and the float are constantly kept in sliding contact with each other, the guide rod and the float are subject to abrasion due to abrasion power in the oil etc., and the abrasion would become even greater due to vibration of the engine. As a consequence, it would become difficult for the float to move up and down, which thereby increases a possibility of malfunction where the float fails to properly follow variation in the oil level.
According to the disclosure of Patent Literature 2, an additional case is mounted in a crankcase, a shaft is provided in such a manner that it extends through upper and lower walls of the additional case and is movable up and down relative to the additional case, the float is provided within the case 20 and threaded over the shaft, the movable contact is provided on the lower surface of the float, and the fixed contacts are provided on a bottom wall of the additional case so as to contact the movable contact as the float descends. Further, an electrically conductive ring is provided on the upper surface of the additional case, and a clip is provided on the upper surface of the float. Thus, the oil level detecting switch disclosed in Patent Literature 2 has a great number of necessary component parts. Therefore, there is a need to reduce the number of necessary component parts from the viewpoint of cost. Further, when an insulating substance, such as dust mixed in the oil, is sandwiched between the movable contact and the fixed contacts, electrical connection between the movable contact and the fixed contacts is prevented, which prevents appropriate oil level detection.